Playing devil's advocate here, but many legal experts were predicting this verdict.
Here's one such article.
You have to understand that the burden of proof was on
the prosecution. The jury did not have to believe Zimmerman's account of the story, they only had to have a reasonable doubt with regards to the prosecution's case that Zimmerman could not have been acting in self-defense. The jury could even believe (and probably did) that Zimmerman was racially profiling Martin when he was following him and still find reasonable doubt.
I think before people start charging the jury as racist, they should remember that the jury has very strict guidelines on how they must reach a verdict and what evidence they need to use. There have been many cases where jurors had a personal opinion that the defendant was guilty but voted not guilty because they had to look at the case in a judicial sense and found reasonable doubt.
At the end of the day, this was a very hard case for the prosecution to prove legally.